Setting up and calibrating apollo twin

[Jtatum2701]

So I'm new to the Apollo Twin and REW and I'm just trying to get all set up. I have chosen universal audio thunderbolt for both input and output. The main output is 1+2 and timing reference output is 3. The main input I have at 1 and loopback I have at 2. I connected an instrument cable from output 3 to input 2 on the back of the apollo. When I calibrate the soundcard the test tone shows -12, the in shows -113, and ref in shows -17.56.
Judging from the tutorials I've seen (none of which mention the difference between "in" and "ref in") I think it's supposed to be playing back through the "in" not "ref in". Any advice on what I'm doing wrong?

 

[John Mulcahy]

Soundcard calibration is for the measurement channel, so connect the loopback to input 1. If you plan to use a loopback connection as a timing reference for measurement that would be connected to the ref input.